Valves are commonly used in process control systems to control the flow of process fluids. Rotary valves (e.g., butterfly valves) typically have a closure member (e.g., a disk) disposed in a fluid path. A shaft operatively couples the closure member to an actuator that rotates the closure member between an open position and a closed position to allow or restrict the flow of fluid between an inlet and an outlet of the valve. When the closure member is rotated to the closed position, the closure member sealingly engages a valve seat or sealing surface (e.g., a seal ring fixed to the valve body) to restrict the flow of fluid through the valve.
A peripheral edge of the closure member is used as a seal contact surface for the valve and must be properly aligned with the sealing surface to effect a proper seal. Thus, to effect a proper seal, it is critical that the closure member be precisely positioned within the valve body so that the peripheral edge of the closure member can sealingly mate or engage the sealing surface. Due to the requirement for precise alignment of the valve closure member relative to the valve sealing surface, rotary valves often cannot be installed in a vertical orientation. In particular, the weight of the valve components or valve trim (e.g., a drivetrain) can cause the closure member to shift and become misaligned with the valve body and sealing surface, thereby comprising the integrity of the seal and causing undesired leakage through the valve (i.e., a quantity of fluid passing through the valve when the valve is in the closed position).